Efficient Conversion of Urea-Based Non-Protein Nitrogen to Microbial Protein: Mechanisms, Regulation and Industrial Prospects

Possessing a high nitrogen content, low cost and stable supply, urea serves as a critical non-protein nitrogen (NPN) source that represents a promising alternative to conventional protein feedstocks for reducing production costs in microbial protein (MP) synthesis. This article systematically discusses the application potential of urea in MP production, the metabolic pathways governing microbial urea utilization, and the key factors influencing the conversion efficiency of urea to microbial protein. Herein, we summarize recent progress in urea modification technologies covering slow-release urea, extruded urea, and urea-based composite preparations and elucidate the complete metabolic mechanisms of urea assimilation in both rumen fermentation and in vitro cultivation, including transmembrane transport, urease-catalyzed hydrolysis, ammonia assimilation, and MP synthesis. Furthermore, we analyze the regulatory effects of dietary energy level, carbohydrate structure, protein concentration, forage quality, urea formulation type, and functional additives on nitrogen utilization efficiency. Current evidence indicates substantial knowledge gaps regarding urea transporter functionality, the coordinated regulation of UC and nitrogen assimilation pathways, microbial community interactions, and the stability control of industrial-scale production. The development of high-efficiency utilization technologies, feed safety evaluation systems, and precision feeding models for industrial applications remains incomplete. This article seeks to provide a thorough theoretical reference for the efficient utilization, mechanistic elucidation, and industrial promotion of urea-based nitrogen sources within MP production systems.